• C Narayana Reddy

      Articles written in Bulletin of Materials Science

    • High field electrical behaviour in lithium–phospho–vanadate glass system

      C Narayana Reddy S Asokan R V Anavekar

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      The high field electrical switching behaviour of lithium–phospho–vanadate glasses has been studied by determining the current–voltage characteristics. The investigated glasses exhibit temperature, thickness and composition dependent trends. At low current, the 𝐼–𝑉 characteristics obey Ohm’s law followed by a negative resistance region where the bulk behaviour dominates and at higher values of current the sample goes to a low resistance state. The studied glasses exhibit memory type switching. It is suggested that electrical switching is due to the formation of conducting channels that are due to electronic origin while thermal effects dominate once the channels are formed resulting in crystallization.

    • A new approach for understanding ion transport in glasses; example of complex alkali diborate glasses containing lead, bismuth and tellurium oxides

      V C Veeranna Gowda C Narayana Reddy K J Rao

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      Mechanism of ion transport in glasses continues to be incompletely understood. Several of the theoretical models in vogue fail to rationalize conductivity behaviour when d.c. and a.c. measurements are considered together. While they seem to involve the presence of at least two components in d.c. activation energy, experiments fail to reveal that feature. Further, only minor importance is given to the influence of structure of the glass on the ionic conductivity behaviour. In this paper, we have examined several general aspects of ion transport taking the example of ionically conducting glasses in pseudo binary, 𝑦Na2B4O7.(1−𝑦) M$_{a}$O$_{b}$ (with 𝑦 = 0.25–0.79 and M$_{a}$O$_{b}$ = PbO, TeO2 and Bi2O3) system of glasses which have also been recently characterized. Ion transport in them has been studied in detail. We have proposed that non-bridging oxygen (NBO) participation is crucial to the understanding of the observed conductivity behaviour. NBO–BO switching is projected as the first important step in ion transport and alkali ion jump is a subsequent event with a characteristically lower barrier which is, therefore, not observed in any study. All important observations in d.c. and a.c. transport in glasses are found consistent with this model.

    • Conductivity studies on microwave synthesized glasses

      Asha Rajiv M Sudhakara Reddy R Viswanatha Jayagopal Uchil C Narayana Reddy

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      Conductivity measurements have been made on 𝑥𝑉2O5 − (100 − 𝑥) [0.5 Na2O + 0.5 B2O3] (where 10 ≤ 𝑥 ≤ 50) glasses prepared by using microwave method. DC conductivity (𝜎) measurements exhibit temperature-and compositional-dependent trends. It has been found that conductivity in these glasses changes from the predominantly ‘ionic’ to predominantly ‘electronic’ depending upon the chemical composition. The dc conductivity passes through a deep minimum, which is attributed to network disruption. Also, this nonlinear variation in 𝜎dc and activation energy can be interpreted using ion–polaron correlation effect. Electron paramagnetic resonance (EPR) and impedance spectroscopic techniques have been used to elucidate the nature of conduction mechanism. The EPR spectra reveals, in least modified (25 Na2O mol%) glasses, conduction is due to the transfer of electrons via aliovalent vanadium sites, while in highly modified (45 Na2O mol%) glasses Na+ ion transport dominates the electrical conduction. For highly modified glasses, frequency-dependent conductivity has been analysed using electrical modulus formalism and the observations have been discussed.

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